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 Post subject: Acer Motherboard problem
PostPosted: Fri Dec 12, 2014 7:54 am 
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Pilgrim
Pilgrim

Joined: Fri Dec 12, 2014 7:30 am
Posts: 3
Hi,

I have an Acer Aspire V3-571G
Motherboard: Q5WVH LA-7912P

Nothing happens when I press the start button and no Led is on when battery is connected.
I have checked some motherboard voltages:
vin is ok, 19V but (see schematic) one pin of PD3 is =0V whereas the other = 19V

Motherboard 1
Motherboard 2
Schematic

My problem is that I don't really know where is PD3, could you tell me if it is possible to replace it please?


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PostPosted: Fri Dec 12, 2014 11:42 am 
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Mobo-fu Master
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Welcome to Motherboards.org.
First rule: Please don't double-post same thread, in same topic folder or other.
As to your problem, the AC adapter or charger has a voltage sensor circuit to prevent over-charging of the battery. If it senses the maximum limit, no current flow. And if no voltage sensed, likely no output.
Some designs have a third contact on the input socket, to disconnect the battery and use only the external power source. Or normally just a two contact socket for input to charge the battery and power the board simultaneously.
Common problem that the solder connections become weak and may break from unwanted movement. Sometimes the foil trace can break at the connection. The outer contact finger in the power socket may be weak or broken.
Then too, contamination from touching the input plug may cause a problem with a positive contact path. Use a slightly damp tissue with alcohol to clean the plug, a cotton swab to clean the socket, if possible.

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PostPosted: Sat Dec 13, 2014 5:42 am 
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Pilgrim
Pilgrim

Joined: Fri Dec 12, 2014 7:30 am
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Fist of all sorry for double post, I didn't want to do this :oops:

Thank you for your response, I have tried with and without battery connected (I know it is not fully charged) and I have measured the same voltages.
In fact my problem happened like this: I had a keyboard problem and wanted to repair it but I have turned on the laptop whereas it was still open (I know I shouldn't have done this :( ). I have moved the keyboard and suddenly the laptop shutdown and I wasn't able to turn it on again.

Do you think it can work if I weld a diode on PD3?

Here is the entire schematic if it can help: http://www.s-manuals.com/pdf/motherboard/compal/compal_la-7912p_r0.4_schematics.pdf

PS: I hope you'll understand what I said since english is not my native language, if something isn't clear, let me know and I'll try to rephrase it.


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PostPosted: Sat Dec 13, 2014 9:49 am 
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Mobo-fu Master
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The PD3 and PD4 are SMD varieties of the 1N4148, a general-purpose diode. The are not mounted in there. Seeing the picture again, all the components from the entire circuit from your first schematic drawing are not mounted on the pictures of your motherboard, most likely this is a stripped-down version of the complete motherboard.

As for the laptop powering down after moving the keyboard, the most likely mishap is you causing a dead short somewhere and killing a few active components in the process.

Repair of the motherboard may prove to be more expensive than simply replacing it.

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PostPosted: Sat Dec 13, 2014 6:02 pm 
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Mobo-fu Master
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Looked at all pages of that service schematic. On the bottom left of page 45, is the circuit concerning "PD3" and "PD4". But note an item labeled as "TP0610K-T1-E3_SOT23-3", a "MOSFET P-CH 60V 185MA" power transistor as its heart. It is designated as item "PQ4" on the circuit board.
In looking at the photo of the PC side of the board, there is no item in that location. Likely an optional feature for a different model, using the same PC board. So no "PD3" and "PD4".

There should be a fuse or fuses surface-soldered on the PC board for the keyboard and touchpad. Possibly noted as an "F1" or similar item. Do a continuity check, no power to the system. Possibly a 2 amp rating, but consult the parts list for exact replacement if bad.
One other thought about the unit not powering on.. possibly in a 'hibernation' state, check the user's manual as to how to undo a possibly frozen feature. But hopefully it will come to life again.

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PostPosted: Mon Dec 15, 2014 10:37 am 
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Pilgrim
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Joined: Fri Dec 12, 2014 7:30 am
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Thank you for your answers, I was a bit disappointed not seeing some components.

So I have measure other pins: (cf.page 47 of the schematic)

- I have ~19V on the 20th pin of PU4 (Vcc) but I have 0V on the 10th pin (ILIM). I wonder if it is normal (no battery plugged, besides I think my battery is dead and I can't charge it).
Is +3VALW delivered by PU4 or another component?
Since it seems to be used to turn on the computer, if I have no voltage... (page 41)

- I also have found this discussion: http://www.badcaps.net/forum/showthread.php?t=29834 and I have tried to measure PQ9 output and I have 0V on pins 1 to 4. Should I have another value?


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